基于均值-方差理论的多阶段公交走廊设计

Phased Transit Service Design Based on Mean-Variance Theory

随机性是公交出行需求的重要特性.随机需求下的公交系统中,不同风险态度(中立风险、规避风险和寻求风险)的决策者会选择不同的设计方案,这在多阶段公交系统走廊设计中更为明显.为研究不同决策风险态度下随机特性对公交服务设计的影响,首先,基于均值-方差理论,提出不同风险态度下的决策方法,并构建对应的多阶段公交走廊设计模型,同时优化不同阶段的公交线路长度、站点选址和发车间隔;之后,利用局部分解法和最优化理论,得出模型的解析解;最后,对不同设计策略(全覆盖设计、单阶段和多阶段的公交线路非全覆盖设计)和风险决策态度下的公交走廊设计进行对比分析.结果表明:1)公交线路多阶段设计具有比全覆盖设计和单阶段设计更低的期望系统成本,以及比单阶段设计更稳定的方案;2)在不同设计策略中,决策风险态度对公交系统的参数配置(即公交线路长度、站点分布和发车间隔)有不同的影响,例如规避风险态度决策者在全覆盖设计中追求更密集的站点分布,而在单阶段设计中则会追求相对更低的站点密度,在多阶段设计中这就更为复杂.该研究从政府管理者和运营商的角度,提供基于需求随机增长下公交系统多阶段设计的风险投资决策方法.

Transit travel demand has an important characteristic of being stochastic.The decision-makers with different risk attitudes(i.e.,risk-neutral,risk-averse,and risk-seeking) will choose various transit service designs in response to the stochastic demand,which seems to be especially critical in the phased transit design.In order to study the impacts of stochastic travel demand on the transit service design,we firstly propose a mean-variance based decision-making approach for decision-makers with different risk attitudes.Correspondingly,the study proposes a model for phased transit corridor design,which can concurrently optimize the line length,transit station location,and headway in each phase.Then,the local decomposition method and optimization theory are adopted to find the analytical solution.Finally,the study compares the transit corridor designs with different design strategies(i.e.,full-covered,once-and-done,and phased designs of the transit line) and risk decisionmaking attitudes.The results indicate:1) the phased design has a lower expected system cost than the full-covered and the once-and-done designs,and a more robust scheme than the once-and-done design;and 2) risk decisionmaking attitudes substantially affect the parameters(i.e.,the transit length,station location,and headway) of transit system under different design strategies;for example,the risk-averse decision-makers tend to seek denser station locations in the full-covered design,but relatively lower station density in the once-and-done design in phased design.The issue becomes more complex in the phased transit design.This study serves to provide a riskbased decision-making model of phased transit service under the increasing stochastic demand for the government manager and transit operators.